The invention is based on a method and to a brake system having a brake booster.
Brake boosters are well known (German application Nos. DE-OS 25 31 264 and DE-OS 31 51 292). In these known brake boosters, one brake circuit is typically closed, and one is open. The open brake circuit is supplied directly with a reservoir pressure fed via a control valve or brake valve. If the pressure supply should fail, the open brake circuit becomes a closed brake circuit. Typically the open brake circuit includes an annular piston, which is mounted on a pedal tappet actuated by the brake pedal.
Two basic types of brake boosters can be identified: those equipped with a travel simulator spring, and those without such a spring, which exerts a perceptible feedback of force to the brake pedal. However, one problem in a brake booster equipped with a travel simulator spring, which is basically superior in its characteristics to a brake booster lacking a travel simulator, is the lack of feedback to the brake pedal of any arbitrary malfunction in the brake circuit. In other words, the driver has no sensation of any malfunction such as the failure of a brake circuit, poor ventilation, vapor bubbles, possible seizing of a control piston acted upon by brake pressure, or the like.
Although in such brake boosters having a travel simulator it is possible to detect malfunctions by the evaluation of piston movements in the brake booster as compared with the movement of the pedal tappet and then to warn the operation of any malfunction via visual and/or acoustical signals, the driver does not necessarily pay attention to such acoustical signals, and he is inclined simply to drive on, without taking care of the problem, unless the malfunction makes itself characteristically and strongly felt during the brake actuation itself.